Thermally Integrated High Power DensitySOFC Generator
Thermally Integrated High Power DensitySOFC Generator
By
FuelCell Energy, Inc.Versa Power Systems, Inc.
At
SECA Annual MeetingPacific Grove, California
April 18-21, 2005
AcknowledgementsAcknowledgements
• ContributorsFCE: Pinakin Patel, Peng HuangVPS: Randy Petri, Brian BorglumGTI: Robert Remick, Kevin KristMSRI/UU: Tad Armstrong, Anil VirkarPNNL: Prabhakar Singh
• Funding Support• DOE-NETL: SECA Program• California Energy Commission• GTI, VPS, FCE
OverviewOverview
• Program Objectives
• Technology Progress- Cell- Stack- System
• Summary
SECA Program ObjectivesSECA Program Objectives
• Develop a kW-class SOFC power plant per SECA goals
• Natural gas as baseline fuel
• Thermal integration for higher efficiency
• Manufacturing cost reduction
• 9-year, 3-phase program
Cell TechnologyCell Technology
• Long Term Testing (VPS)
• Modeling (PNNL)
• Cathode Development (MSRI-UU)
• Sulfur Tolerance (MSRI, GTI)
• Redox Tolerance (MSRI, VPS)
26,000 hours of Operation
Trend DataTest #10545; (Long Term Test: TSC1, 10 x 10 cm2)Test Stand #6, January 9, 2002 - January 10, 2005
0.000
0.200
0.400
0.600
0.800
1.000
0 5000 10000 15000 20000 25000Elapsed Time, h
Volta
ge, V
Test Conditions:750°C, 556 mA/cm2 389 mA/cm2
54% fuel utilization: 630 439 mlpm H2, 630 439 mlpm N2, 3% H2O 27% air utilization: 3000 2092 mlpm air
Degradation rate: 1.3% per 1000 h
(11 mV per 1000 h)
Long Term Cell TestingLong Term Cell Testing
SS Cross Flow Interconnects
PNNL ModelingPNNL Modeling
Sulfur Tolerance of AnodesSulfur Tolerance of Anodes
•Tested at 800 °C
•Cycled between H2 and H2 with 10ppm H2S
• Anode tested with 1, 5, 10, and 100 ppm H2S in fuel
• Performance degradation of ~6% with 10 ppm H2S
• Degradation rate decreases with time until equilibrium is established
• Complete recovery with sulfur free fuel
• No permanent degradation or failure of anode observed
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700700
710
720
730
740
750
760
770
780
Vol
tage
(mV
)
Time (h)
Start H2Start H2
Start 10ppmStart 10ppm
Start 10ppm
Start 10ppm
Start H2
Start H2
Start 5ppmStart 10ppm
Start H2
Start H2
580
590
600
610
620
630
640
650
660
670
680
650.0 700.0 750.0 800.0 850.0 900.0 950.0 1000.0 1050.0
Time (Hours)
Pote
ntia
l (m
V) @
30
0mA
/cm
²
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
% M
etha
ne C
onve
rsio
n
Performance CH4 Conv.
Fuel: 76.3% H2, 19.5% CO2, 4.2% CH4Oxidant: 100% AirSingle Cell Active Area: 96cm² Fuel Utilization: 45% @ 300mA/cm² Oxidant Utilization: 30% @ 300mA/cm² Anode Dew Point: 73°C ( S/C Ratio: 2.3)Cathode: DryOperating Temperature: 800°COperating Pressure: 1 atm
Start Injection of 2.6 ppm H2S
Stop H2S
Cell On OCV
Performance Decay due to H2S Poisoning
Performance Recovery
Effect of H2S Poisoning on Cell PerformanceEffect of H2S Poisoning on Cell Performance
Stack TechnologyStack Technology
• Stack Design for Greater Output (VPS)
•Triple Mode Cooling (VPS-FCE)
• Radiative Cooling (CEC Program)
• Thermal Cycling (MSRI, VPS)
• Gasket Development (MSRI, FCE, VPS)
Stack Design For Greater Power OutputStack Design For Greater Power Output
112-cell single tower with 4 stack modules
84-cell single tower with 4 stack modules
3800 W DC gross BOL2600 W DC gross BOL
0.36 A/cm20.33 A/cm228-cell stack module21-cell stack module
3-1 StackAurora Stack
50% Increase In Stack Power
Benefits of Triple Mode Cooling:2 kW Aurora System
Benefits of Triple Mode Cooling:2 kW Aurora System
0
200
400
600
90100200300
500
0
4
8
12
Air Air + DIR Air + DIR+ Radiative
Reg
en. A
irH
EX S
ize
Blo
wer
Pow
er, W
Air
Flow
,SL
PMN
et E
lect
rical
Effic
ienc
y, %
CoolingMode
Higher Efficiencyand
Reduced BOP Cost
25
30
35
40
400
Impact Of DIR On Cell TemperaturesImpact Of DIR On Cell Temperatures
Temperature mapping performed on middle cell of a 5-cell, 121 cm2 active area stack with city natural gas
• 0-25% DIR has high DT: hot spot at AO/FI corner
• 75%-100% DIR has high DT: cold spot at AI/FI
• 50% DIR has lowest DT: optimal voltage vs. degradation balance
Stack Operation With 100% Methane DIRStack Operation With 100% Methane DIR
0
0.2
0.4
0.6
0.8
1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Current density (A/cm2)
Volta
ge p
er c
ell (
V)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Pow
er d
ensi
ty (W
/cm
2 )
H2CH4
• Steam to carbon ratio of 2:1
• 60%Uf / 50% Uo
• 10-cell stack, 92 cm2 active area per cell
• Tested at 800oC
CEC Project: Radiative CoolingCEC Project: Radiative Cooling
• Goals: Prove concept of radiant air pre-heaters at multi-kilowatt sizes (Higher power density, Lower operating temperature, Lower costs)
• Design 10 kW power module
• RAP/Stack module Tests at GTI and MSRI
• Kevin Krist of GTI will Present CEC Progress on Wednesday at 4:30 pm
Radiative Cooling For Stack Radiative Cooling For Stack
RAP Panels
• Preheat Air With Radiation FromStack (RAP)
• Decreased Thermal Stresses
• Reduced Cooling Air Flow
Thermal Cycling of Stacks Thermal Cycling of Stacks
• 5-cell stack
• Tested at 800 °C
• Newly developed metal seal
• 98% sealing efficiency of hydrogen gas
0
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0.9
1
1.1
1.2
0 2 4 6 8 10 12
Number of thermal cycles
Volta
ge (V
)
OCV Voltage @ 0.375 A/cm2
1.06 V
0.7 V
Stack Repeat Unit Testing – 50 Thermal Cycles over 5000 hoursStack Repeat Unit Testing – 50
Thermal Cycles over 5000 hoursGlob 101196
Oven #18, (September 23, 2003 - April 26, 2004)
0.000
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1.000
0 1200 2400 3600 4800 6000Elapsed Time, h
Volta
ge, V
TC's 1-5 TC's 41-50TC's 30-40TC's 19-29
TC's 9-18TC 8
TC 7
TC 6
Test stand
Test stand
Test standTest stand
Test stand
Degradation Rate: 2.5 mV/Thermal Cycle
T = 750°CI = 500mAcm-2Uf = 50%Ua = 25%
Gasket Test FacilityGasket Test Facility
Gasket
Compression System(Active, Pneumatic)
Set Up for Controlled Test Conditions
Normalized Gas Leak Rates of PH-2 GasketNormalized Gas Leak Rates of PH-2 Gasket
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 5 10 15 20 25 30 35Differential Pressure (Inch water)
Norm
aliz
ed L
eak
Rate
(Scc
m/(c
m.m
in) Helium
AirMica in Air
An Order of Magnitude Better Than Mica Gasket
Composite Gasket: Performance on HeliumComposite Gasket: Performance on Helium
0
1
2
3
4
5
6
7
8
9
10
0 500 1000 1500 2000 2500 3000Hours
Leak
Rat
e of
Hel
ium
(Scc
m/m
in) 127 mm (5 inch) water
254 mm (10 inch) water
Gasket inner size: 10x10 cm.For cell w ith 10x10 cm active area, given - 500mA/cm2 - Fuel Uf: 75% - Helium f low rate: 500 ml/min99% seal eff iciency: leak rate 5 ml/min
Goal: 99% seal efficiency
Stable Seals for the 3000-hour Test
Trend Data,Glob 10920(Glass Seal: 50% Fuel Utilization, 25% Air Utilization, 0.5 A/cm2, 10 x 10 cell)
Oven #3, (October 2, 2002 - January 3, 2004)
0.0000.1000.2000.3000.4000.5000.6000.7000.8000.9001.0001.100
0 1200 2400 3600 4800 6000 7200 8400 9600 10800 12000
Elapsed Time, h
Volta
ge, V
Degradation rate is approximately 1% per 1000 h (11 mV per 1000 h)
Single Cell Longevity Testing of Glass-Ceramic Seal - 750ºC
Single Cell Longevity Testing of Glass-Ceramic Seal - 750ºC
Advantage of Glass Seals = Hermetic fuel cavity
System DevelopmentSystem Development
• Basis: Natural Gas Fuel, Grid Parallel Operation
• Aurora System with Radiative HEX (2 kW- net AC)
• Baseline System (3 kW-net AC)
• Advance System (10kW-net AC)
Aurora & 3-1 Hot Power Module& T/C Layout
Aurora & 3-1 Hot Power Module& T/C Layout
A i r I n A i r O u t
Air In
Air Out
FI
AO AI
FO
SOFC Stack
RadHEX
Aurora hot power modulewithout RadHEX
Aurora hot power modulewith RadHEX
Black ‘dots’ denotethermocouple locations
Aurora System Operation On Natural GasAurora System Operation On Natural GasSt
ack
Tow
er V
olta
ge, V
olts
Grid Parallel Operation for 1600 + hours02-Feb-05 to 05-Apr-05
Scale-up to 3 kWScale-up to 3 kW
3 kWnet system commissioning
underway
3 kWnet System“3-1”
2 kWnet System“Aurora”
FT
FT
Anode In
FROM PROCESSAIR #1
Radiative AirExchanger
Cathode InFROM PROCESS
AIR #2
Radiative FuelHeat Exchanger
Stack Zone
FROM PROCESSFUEL
SYSTEM EXHAUST
ZnOPreOx HDS
RegenerativeFuel HeatExchanger
Anode Out
Cathode Out
HDS Subsystem
Warm FuelRecycle Blower
SolidOxide
Fuel CellStack
RecycleCooler
FR 2
I
2
To Recycle Cooler
Integrated Module
TO 1
10 kW Concept Design
10 kW Advance System10 kW Advance System
Parker Blower to be Used as a Baseline Parker Blower to be Used as a Baseline
Developed for use with PEM Fuel CellsMaximum Temperature Rating of
120°C
Regenerative Fuel HXRegenerative Fuel HX
• Current Specifications call for a working range of 750°C inlet to 200°C outlet.
• Four vendors have been identified– Small size is a problem – not a typical
product– Temperature range limits manufacturing
methods to welding – not brazing– Small initial sales volume is a problem for
cost reduction
Hydrocarbon VariabilityHydrocarbon Variability
1000 to 1050970 to 1200HHV Btu/SCF0 to 2%0 to 2%CO2
0 to 3%0 to 10%Nitrogen
Odorant Analysis: Natural Gas at NETLOdorant Analysis: Natural Gas at NETL
0.574.64
OthersTotal
1.14Thiophane0.29Thiophene0.13Dimethyl Disulfide0.97Diethyl Sulfide0.84Methyl Ethyl Sulfide0.23Dimethyl Sulfide (DMS)0.37T-Butyl Mercaptan0.10Ethyl Mercaptan
PPMVComponent Name
ImpuritiesImpurities
0 to 80.5 to 10H2O, lb/MMSCF
2 to 12 ppmv2 to 17 ppmvTotal Sulfur
2 to 10 ppmv2 to 12 ppmvOdorants
80% RangeFull RangeComposition
Odorant RemovalOdorant Removal
• Copper impregnated adsorbents work well but have a low capacity for DMS.
• Mole sieve adsorbents for DMS are expensive.
• Hydrodesulfurization (HDS) could be a universal odorant removal system but it requires hydrogen, doesn’t handle unsaturated hydrocarbons well, and will overheat if propane-air is injected.
SummarySummary
• Single Cell Operation using SS Interconnects Demonstratedfor 26,000 hours (Degradation Rate: 1.3% per 1000 hr)
• Performed 50 Thermal Cycles in a Stack Repeat Unit During 5000hours of Operation
• Work Initiated in Improving Redox and Sulfur Tolerance of theAnode Verified
• The 112 cell Stack Tower Showed a 50% Increase in PowerOutput(3.8 kW/Stack Tower)
• Aurora System Operated for 1600 + hours on Natural Gas Fueland in Grid Parallel Mode
Approach to Advanced CathodesApproach to Advanced Cathodes• Novel materials.
• Transport and adsorption properties; focus on materials with strong tendency for oxygen adsorption.
• Particle size and morphology; inter-particle contact.
• Microstructure stability at elevated temperatures.
• Introduction of electro-active species by infiltration.
• Identification of electro-activematerials using patterned electrodes.
Electrolyte Electrolyte
Introduction ofaqueous saltsolutions intoporous cathode
Firing to form nanosizeparticles of electro-activematerials
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.50.0
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1.2
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1.6
2.0
2.4
0.15Ωcm2 0.12Ωcm2
0.13Ωcm2Vol
tage
(V)
Current Density (A/cm2)
0.72Ωcm2
Pow
er D
ensi
ty (W
/cm
2 )
1infil 2infil 3infil 4infil
~1.7W/cm2
@ 0.7V
Performance of a button cell (2 cm2 cathode) at 800oC
Patterned Electrodes – Impedance Spectroscopy – Charge Transfer Resistivity
Patterned Electrodes – Impedance Spectroscopy – Charge Transfer Resistivity
Patterned Electrodes
Impedance spectra at various pO2
Charge transfer resistivity as a functionof temperature and pO2
Collaborative work: University of Utahand PNNL
Development of Redox Tolerant AnodesDevelopment of Redox Tolerant Anodes
• Standard Ni-YSZ anodes tested for redoxtolerance
• Tested at 600-800 °C
• Cells mechanically fail– Electrolyte microcracks– Anode support weakened– Some delamination
• Mechanism: expansion of Ni during oxidation microcracks YSZ in anode Microcracking
As-sintered Reduced Reoxidized
Development of Redox Tolerant AnodesDevelopment of Redox Tolerant Anodes• New anode compositions have been developed
• Exhibit better redox tolerance– Anode support mechanically intact after redox cycling– No microcracking of electrolyte– Delamination has been suppressed
• Future work – Improve anode strength after deep redox cycles– Optimize compositions and microstructure
Glass-Ceramic Seal Thermal Cycling Testing – 750°C
Glass-Ceramic Seal Thermal Cycling Testing – 750°C
7597927801.08025
7537937831.07315
7598017941.0725
7598037991.0781
7487957881.0780
0.5A/cm2, 70% Uf, 35% Ua
0.5A/cm2, 50% Uf, 25% Ua
0.74A/cm2, low Uf
Open Circuit
Thermal Cycle
Number
Cell Voltage (mV) at
Limited Rights Data
Sealing in SOFC
• Thermal, chemical and mechanical stability to stack components and conditions
• Within designed leakage tolerance over the life of the stack at both steady state and transient operating conditions
• More than 30% to allow deformation for stack assembly requirements
Gastight
Compressibility
Dielectric Stability
Development of a high temperature seal
requires integrated solutions to these
requirements
Sealing Requirements in SOFCSealing Requirements in SOFC
• More than 105 ohm·cm to avoid possible current leakage and cell shortening
• Thermally and mechanically robust
• Flexible configuration
• Tape cast, easy manufacturing, and low cost
0.0
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0.5
0.6
0 20 40 60 80 100 120 140Spring load (psi)
H2 l
eak
rate
(cc/
min
-cm
)
Composite AComposite B
800oC, H2 gas maintained at 4 kPaGreen tape of MSRI composite seal
Composite Seal TestComposite Seal Test